They should match your interior trim.
This color will also allow you to make more decorating changes in the future. Such as draperies.
bring one home and try it (b-4 the cutting) sometimes the contrast can be nice or it can just make your trim look dirty but the only way to truly tell is in your home with your lighting.
You might as well match it to the interior trim. When you look at the blinds from the inside, you see them clearly. But, when looking at the blinds from the outside, the glass from the window might distort the color a bit, making them look off-white, anyway.
Besides, you’ll be looking at them from inside all the time, and occasionally from the outside. So, make it match from the side you will see all the time.
i would go with the off white… i bought the same ones at home depot and they are great.. and easy to put up